HOW TO DETERMINE DISSOLVED OXYGEN IN WATER (WINKLER METHOD)

DETERMINATION OF DISSOLVED OXYGEN IN WATER (WINKLER METHOD)

AIM:
To determine the dissolved oxygen (DO) content in water.

APPARATUS:
BOD bottles, burette, pipette.

REAGENT:
Manganese sulfate, alkaline iodide, starch, sodium thiosulphate.

PRINCIPLE:
DO oxidizes Mn²⁺ to Mn⁴⁺, which liberates iodine that is titrated.

PROCEDURE:

• Add MnSO₄ and alkaline iodide to water sample.

• Allow precipitate to form and settle.

• Add H₂SO₄ to dissolve.

• Titrate liberated iodine with sodium thiosulphate using starch as indicator.

CALCULATION:
DO (mg/L) = Volume of thiosulfate used × Normality × 8